Final answer:
The collection tube that contains thixotropic gel is the gold top tube, which aids in serum separation during blood processing.
Step-by-step explanation:
The gold top tube is the collection tube that contains thixotropic gel. This type of gel is used in blood collection tubes to facilitate the separation of the serum from blood cells after centrifugation. Thixotropic gels have the property of becoming less viscous when agitated and returning to a more viscous state when standing, which helps in creating a barrier between the serum and the cells once the sample has been centrifuged.